Method and apparatus for cleaning wells



March 10, 195 9 I 'r. W. McsPADpEN 2,376,842.

'METHOD AND. APPARATUS FOR CLEANING WELLS Filed Sept. 27. 1954 THOMAS w. MCSPADDEN IN V EN TOR.

' ATTORNEY United States Pat n NLETHOD AND APPARATUS FOR CLEANING WELLS Thomas W. McSpaddeu, American Petroleum Delaware Application September 27, 1954, Serial No. 458,380 7 Claims. (Cl. 166-43) Tulsa, Okla., assignor to Pan Corporation, a corporation of application Serial Number 203,420, filed December 29,

1-950, and now abandoned, is directed, in general, to

the mechanical method of removing such deposits from oil well tubing or the like and is more particularly directed to the removal of such deposits with a plug which is soluble in the fluid produced by the well.

It is an object of this invention to provide an improved method for removing a deposit from the inside of a conduit. Another object of this invention is to provide a very inexpensive oil-soluble plug of improved design which cannot permanently plug a well tubing, a well flow line or similar oil conduits, and which will clean such conduits better than oil-soluble plugs which have been used heretofore. Other objects of this invention will become apparent from the following description. In this description, reference will be made to the accompanying drawing which shows a cross-sectional view of a well including means for removing a deposit from the inside of the tubing in accordance with this invention.

According to this invention, a plug having a minimum diameter equal to about the nominal diameter of an oil conduit such as well tubing and made from a micro crystalline wax, preferably a petroleum ceresin wax, is driven down through the tubing by connecting the highpressure gas in the annular space surrounding the tubing with the tubing above the plug. The plug, if not previously dissolved by the oil, is then returned to the surface by flowing the well. Referring now more specifically to the drawing, the casing 10 of a well has an outlet 11 at the surface. The oil conduit, tubing 12, containing a deposit 13 of parafiin, scale, or the like, is suspended inside casing 10 from a tubing head 14. A master valve 15 is attached to the upper end of tubing head 14. A flow cross 16 is connected to the upper end of master valve 15. This cross is provided with a flow line outlet 17 which may be closed by valve 18. The cross also contains a by-pass line outlet 19. The upper end of cross 16 is fitted with a bull plug 20 into which is welded a sleeve 21 having perforations 22. This sleeve has substantially the same inside diameter as tubing 12, for reasons hereinafter shown. A by-pass line 23 containing a by-pass valve 24 is connected between casing outlet 11 and by-pass line outlet 19.

In operation, the well is shut in by closing master valve 15 and flow line valve 18. Bull plug 20 is then unscrewed from cross 16 and plug 25 introduced into the top of master valve 15. By-pass valve 24 and master valve 15 are then opened so that the gas in the annular space between tubing 12 and casing 10 forces the plug down the tubing. In flowing wells, the casing pressure is greater (200-500 pounds or more) than the tubing 2,876,842 Patented Mar. 10, 1959 pressure, so that plug 25 is forced down the tubing, removing the deposit 13. The wax, scale, or the like removed from the inside surface of the tubing is then returned with the plug 25 to the surface when flow line valve 18 is opened to flow the well. Since the material forming plug 25 is normally only slowly soluble in well fluids, the remainder of the plug, i. e., that which has not been dissolved, is lifted by the well fluids when the well is produced into the perforated sleeve 21 through which the well fluids pass to the well flow line. There, the warm well fluids flowing over the plug slowly dissolve it and carry the constituents to the stock tank with the well fluids.

One method of operation I have found particularly satisfactory is, at the end of a days run, to close the master gate and the flow line valve, remove the bull plug, deposit the wax plug in the well head above the master valve, insert the bull plug and open the master gate and bypass valve. The plug is then driven over night down through the tubing and the deposit. The next day the by-pass valve is closed and the well is put on production as usual. I have also found that, even in the wells which produce the worst paraffin deposits, these plugs can be run at intervals of from several days to several months. That is, even major accumulations of scale or paraflin can be removed by hard microcrystalline wax plugs of the type above described.

With regard now to the composition of plug 25, I have found that microcrystalline wax has properties substantially superior to other oil-soluble compounds which have been used'to scrape deposits from oil well tubing. The

preferred Waxes, the petroleum ceresins are, in general, the hard, microcrystalline waxes which are substantially oil free and which have a melting point of about F. or higher, preferably between about and F.

These petroleum ceresins, which have a molecular weight of greater than about 450 and a penetrometer value by the ASTM method D5-25 of less than 25, are particularly suited to the removal of semi-solid or solid deposits from well tubing. Softer materials, such as rubber compounds, slack wax, sweat wax, and other soft paraflin waxes, appear to flow like viscous fluids through a tubing and therefore to extrude through deposits having an inside diameter much smaller than the initial diameter of the plug. In one case, for example, a relatively-soft, one-inch diameter, commercial plug made from rubber and a resin was driven through a one-inch pipe, and the extruded paraifin was only about one-half inch in diameter.

In another case, the petroleum paraflin removed from a deposit in a well flow line was formed into a plug and forced through a pipe containing an annular paraflin deposit. This plug, like the rubber and resin plug, was swedged down to the minimum diameter of the parafiin deposit and passed through the pipe without removing the deposit. Microcrystalline waxes such as petroleum ceresins, on the other hand, have been found to behave more like plastics than like viscous fluids and have a considerably retarded tendency to extrude through tubing deposits. Harder materials, such as naphthalene or moth balls, have been proposed, but I have found that these materials are brittle and are quite often disintegrated or broken as they are forced through the tubing at high velocity. Microcrystalline waxes are, however, like these materials in that they are soluble in the hydrocarbon well fluids, so that when a plug becomes lodged in the tubing it can be removed by flowing the well and dissolving away the plug.

Microcrystalline wax is distinguishable from ordinary paraffin wax in a number of respects. The molecular weight of paraflin waxes ranges from about 360 to 420 while the molecular weight of microcrystalline wax; typically falls in the range from about 580 to about 1000.

Paraflin waxes consist mainly of straight chain molecules while the microcrystalline waxes which contain some straight chain molecules also contain a large proportion of branched chain molecules. Many such tests have been proposed to distinguish microcrystalline waxes from parafiin. A preferred test is a comparison with the microscope or with microphotographs. See, for example, the paper, Microcrystalline Waxes, Their Manufacture,

Properties and Uses in the Paper Industry, published in the February 1946 issue of The Paper Industry and Paper World.

The microcrystalline wax plugs are preferably cylindrical and have a length only slightly greater than the diameter. The plug preferably has-one end, the leading end rounded at the corners, as indicated in the drawing, to facilitate passage through reasonably sharp bands, such as ells and the like, and through a tubing string having spaces at the collars which often stop a flat-nosed plug. Petroleum ceresins and other microcrystalline waxes being a common commodity and very inexpensive, plugs of the type described can be produced for a very nominal expense by merely heating the wax to its melting point and casting it or otherwise extruding the wax, after being heated to the softening point, into long cylinders of the proper diameter which can be subdivided into plugs 'of the proper length.

It will be apparent that, while a microcrystalline wax plug is particularly adapted to removing deposits from a well tubing, such plugs can also be used to advantage in well fiow lines, petroleum pipe lines, and the like. The invention is therefore subject to a wide variety of modifications and uses, and such modifications which fall within the scope of the appended claims are intended to be within the scope and intent of the invention.

I claim:

1. A plug for removing paraflin from a conduit consisting essentially of a hard substantially oil-free microcrystalline wax, said plug having a minimum cross-sectional area conforming to the cross-sectional area of said conduit.

2. A plug according to claim 1 wherein said wax has a melting point greater than about 160'F.

3. A plug for removing parafiin from the wall of a 4 conduit through which oil flows including sufficient hard substantially oil-free microcrystalline wax to render said plug plastic and soluble in said oil, said plug having a minimum cross-sectional area conforming to the crosssectional area of said conduit and said wax being slowly oil soluble whereby said plug can be removed from said conduit by circulating an oil solvent thereby.

4. A plug according to claim 3, said plug being cylindrical and having a diameter substantially equal to the diameter of said conduit and a length at least as great as said diameter.

5. A plug according to claim 4 wherein said microcrystalline wax has a melting point greater than about 160 F.

6. A plug for removing parafiin from a conduit through which oil flows consisting of a cylinder of hard substantially oil-free microcrystalline wax, said cylinder having a minimum cross-sectional area substantially equal .to the cross-sectional area of said conduit.

7. A method of cleaning a parafiin deposit'from'the walls of a well tubing comprising the steps of introducing a'hard substantially oil-free microcrystalline wax plug into the top of said tubing, said plug having substantially the, diameter of said tubing and a length at least as great as said diameter, forcing said plug down saidtubing to scrape said deposit from said walls by applying a differential pressure across said plug and subsequently flowing said well to remove said deposit and said plug from'sa'id tubing.

References Cited in the file of this patent UNITED STATES PATENTS 1,790,450 Torrance Jan; 27, 1931 2,058,825 Rallet ct a1 Oct. 27,1936 2,352,805 Scheuermann et al "July 4, 1944 2,411,044 Landrum et al Nov; 12, 1946 2,603,804 Bilhartz et a1 -Iu1y 22, 1952 2,744,770 Brown May 8,1956

OTHER REFERENCES The Chemistry and Technology of Waxes by Warth. Reinhold Publishing Co., N. Y., 1947, page 243, copy'in Div. 31. 

1.FIG-01 A PLUG FOR REMOVING PARAFFIN FROM THE WALL OF A CONDUIT THROUGH WHICH OIL FLOWS INCLUDING SUFFICIENT HARD SUBSTANTIALLY OIL-FREE MICROCRYSTALLINE WAX TO RENDER SAID PLUG PLASTIC AND SOLUBLE IN SAID OIL, SAID PLUG HAVING A MINIMUM CROSS-SECTIONAL AREA CONFORMING TO THE CROSSSECTONAL AREA OF SAID CONDUIT AND SAID WAX BEING SLOWLY OIL SOLUBLE WHEREBY SAID PLUG CAN BE REMOVED FROM SAID CONDUIT BY CIRCULATING AN OIL SOLVENTTHEREBY.
 7. A METHOD OF CLEANING A PARAFFIN DEPOSIT FROM THE WALLS OF A WELL TUBING COMPRISING THE STEPS OF INTRODUCING A HARD SUBSTANTIALLY OIL-FREE MICROCRYSTALLINE WAX PLUG INTO THE TOP OF SAID TUBING, AND PLUG HAVING SUBSTANTIALLY THE DIAMETER OF SAID TUBING AND A LENGTH AT LEAST AS GREAT AS SAID DIAMETER, FORCING SAID PLUG DOWN SAID TUBING TO SCRAPE SAID DEPOSIT FROM SAID WALLS BY APPLYING A DIFFERENTIAL PRESSURE ACROSS SAID PLUG AND SUBSEQUENTLY FLOWING SAID WELL TO REMOVE SAID DEPOSIT PLUG FROM SAID TUBING. 